at the Bureau of Engraving and Printing on the Giori presses, the stamp shares numerous design elements with USA Scott 1557, the Mariner 10 Issue of 1975. Mariner 10 Issue of 1975 Engineered to explore the orbits of Venus and Mercury, Mariner 10 launched in November 1973. The mission's two- year plan used the gravitational pull of Venus to reach Mercury. The probe also used solar winds to help with locomotion when fuel ran low. Mariner 10 orbited the planets in the opposite direction of Earth's orbit. Mariner's first photographed images, which revealed Venus's dense cloud cover, reached NASA scientists in February 1974. Data collected by Mariner 10 helped determine Venus's rotation period and use of Earth's magnetic field. Photos of Mercury revealed its cratered surface and its large scarps and plains. Research also recorded its radical temperature variations between night and day. The 10-cent Mariner 10 commemorative stamp was issued on April 4, 1975, at Pasadena, California. It paid the domestic first-class rate for letters weighing less than a half ounce. The stamp shares numerous design elements with USA Scott 1556, and while they have different designers and dates of issue, the two are cataloged together under the heading "U.S. Unmanned Accomplishments in Space." Designed by Roy Gjertson, the Mariner 10 commemorative postage issue was printed at the Bureau of Engraving and Printing in multi-color on the Giori presses. Quantities issued totaled more than 158 million. Apollo–Soyuz Commemorative Issue of 1975 With the Apollo–Soyuz mission, two nations collaborated on a space project for the first time. In July 1975, the United States launched the manned Apollo Command module to rendezvous with Russia's manned Soyuz module. A special docking station facilitated interaction among the astronauts. Television stations worldwide broadcast the historic docking and bi-national greeting made by the astronauts. The modules remained docked for two days, during which the teams performed numerous experiments. The U.S. Postal Service issued this se-tenant pair of two 10-cent multicolored stamps on July 15, 1975, at Kennedy Space Center, Florida. Inexplicably, the circular program insignia on the left-hand stamp is rotated to the Soviet configuration, showing the red Soyuz section on the left. The Soviet Union also released stamps of similar design (Russia Scott 4339–4340) at the same time. This denomination paid the domestic first-class rate for letters weighing less than half ounce. Robert T. McCall designed the 'after link-up' image, and Anatoly Aksamit designed